Three trials were conducted in the spring of 1985 to evaluate the
effectiveness of MGA feeding and Prostaglandin (PGF) injection on estrus
induction and synchronization. Trials 1 and 2 were both done on a Kansas ranch
and involved 70 heifers and 86 cows, respectively. In both trials, all cycling and
non-cycling females were fed MGA (7 days in trial 1, 9 days in trial 2) and half of
the cows and heifers received a PGF injection. The estrus response was higher
(P<.0l) for the cycling heifers with the combination treatment. Both treatments
resulted in similar first service conception rates and both were effective in
inducing estrus in noncycling heifers. Only a small percentage of the cows in trial
2 were cycling prior to the treatments and only a small percentage of the
non-cycling cows responded to the MGA.
In trial 3, half of the cycling heifers were fed MGA for 7 days and PGF
was injected on day 7. Response to synchronization peaked 96 to 120 hr following
MGA withdrawal. Among F1 Angus X Hereford heifers, the MGA-PGF treatment
reduced (P<.0l) first service conception rates as compared to controls (55 vs 80%),
although a reduction was not seen with F Brahman X Hereford heifers.
Conversely, 45-day pregnancy rates tended to be higher among both groups of
synchronized heifers (P>.05). The MGA treatment also initiated cyclicity in
prepuberal females of both crosses.
